// SPDX-License-Identifier: GPL-2.0
/* kernel/rwsem.c: R/W semaphores, public implementation
 *
 * Written by David Howells (dhowells@redhat.com).
 * Derived from asm-i386/semaphore.h
 *
 * Writer lock-stealing by Alex Shi <alex.shi@intel.com>
 * and Michel Lespinasse <walken@google.com>
 *
 * Optimistic spinning by Tim Chen <tim.c.chen@intel.com>
 * and Davidlohr Bueso <davidlohr@hp.com>. Based on mutexes.
 *
 * Rwsem count bit fields re-definition and rwsem rearchitecture by
 * Waiman Long <longman@redhat.com> and
 * Peter Zijlstra <peterz@infradead.org>.
 */

#include <generated/deconfig.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/sched/rt.h>
#include <linux/sched/task.h>
#include <linux/sched/debug.h>
#include <linux/sched/wake_q.h>
#include <linux/sched/signal.h>
#include <linux/sched/clock.h>
#include <linux/export.h>
#include <linux/rwsem.h>
#include <linux/atomic.h>

#include "lock_events.h"

///*
// * The least significant 3 bits of the owner value has the following
// * meanings when set.
// *  - Bit 0: RWSEM_READER_OWNED - The rwsem is owned by readers
// *  - Bit 1: RWSEM_RD_NONSPINNABLE - Readers cannot spin on this lock.
// *  - Bit 2: RWSEM_WR_NONSPINNABLE - Writers cannot spin on this lock.
// *
// * When the rwsem is either owned by an anonymous writer, or it is
// * reader-owned, but a spinning writer has timed out, both nonspinnable
// * bits will be set to disable optimistic spinning by readers and writers.
// * In the later case, the last unlocking reader should then check the
// * writer nonspinnable bit and clear it only to give writers preference
// * to acquire the lock via optimistic spinning, but not readers. Similar
// * action is also done in the reader slowpath.

// * When a writer acquires a rwsem, it puts its task_struct pointer
// * into the owner field. It is cleared after an unlock.
// *
// * When a reader acquires a rwsem, it will also puts its task_struct
// * pointer into the owner field with the RWSEM_READER_OWNED bit set.
// * On unlock, the owner field will largely be left untouched. So
// * for a free or reader-owned rwsem, the owner value may contain
// * information about the last reader that acquires the rwsem.
// *
// * That information may be helpful in debugging cases where the system
// * seems to hang on a reader owned rwsem especially if only one reader
// * is involved. Ideally we would like to track all the readers that own
// * a rwsem, but the overhead is simply too big.
// *
// * Reader optimistic spinning is helpful when the reader critical section
// * is short and there aren't that many readers around. It makes readers
// * relatively more preferred than writers. When a writer times out spinning
// * on a reader-owned lock and set the nospinnable bits, there are two main
// * reasons for that.
// *
// *  1) The reader critical section is long, perhaps the task sleeps after
// *     acquiring the read lock.
// *  2) There are just too many readers contending the lock causing it to
// *     take a while to service all of them.
// *
// * In the former case, long reader critical section will impede the progress
// * of writers which is usually more important for system performance. In
// * the later case, reader optimistic spinning tends to make the reader
// * groups that contain readers that acquire the lock together smaller
// * leading to more of them. That may hurt performance in some cases. In
// * other words, the setting of nonspinnable bits indicates that reader
// * optimistic spinning may not be helpful for those workloads that cause
// * it.
// *
// * Therefore, any writers that had observed the setting of the writer
// * nonspinnable bit for a given rwsem after they fail to acquire the lock
// * via optimistic spinning will set the reader nonspinnable bit once they
// * acquire the write lock. Similarly, readers that observe the setting
// * of reader nonspinnable bit at slowpath entry will set the reader
// * nonspinnable bits when they acquire the read lock via the wakeup path.
// *
// * Once the reader nonspinnable bit is on, it will only be reset when
// * a writer is able to acquire the rwsem in the fast path or somehow a
// * reader or writer in the slowpath doesn't observe the nonspinable bit.
// *
// * This is to discourage reader optmistic spinning on that particular
// * rwsem and make writers more preferred. This adaptive disabling of reader
// * optimistic spinning will alleviate the negative side effect of this
// * feature.
// */
//#define RWSEM_READER_OWNED	(1UL << 0)
//#define RWSEM_RD_NONSPINNABLE	(1UL << 1)
//#define RWSEM_WR_NONSPINNABLE	(1UL << 2)
//#define RWSEM_NONSPINNABLE	(RWSEM_RD_NONSPINNABLE | RWSEM_WR_NONSPINNABLE)
//#define RWSEM_OWNER_FLAGS_MASK	(RWSEM_READER_OWNED | RWSEM_NONSPINNABLE)

//#ifdef CONFIG_DEBUG_RWSEMS
//# define DEBUG_RWSEMS_WARN_ON(c, sem)	do {			\
//	if (!debug_locks_silent &&				\
//	    WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, magic = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
//		#c, atomic_long_read(&(sem)->count),		\
//		(unsigned long) sem->magic,			\
//		atomic_long_read(&(sem)->owner), (long)current,	\
//		list_empty(&(sem)->wait_list) ? "" : "not "))	\
//			debug_locks_off();			\
//	} while (0)
//#else
//# define DEBUG_RWSEMS_WARN_ON(c, sem)
//#endif

///*
// * On 64-bit architectures, the bit definitions of the count are:
// *
// * Bit  0    - writer locked bit
// * Bit  1    - waiters present bit
// * Bit  2    - lock handoff bit
// * Bits 3-7  - reserved
// * Bits 8-62 - 55-bit reader count
// * Bit  63   - read fail bit
// *
// * On 32-bit architectures, the bit definitions of the count are:
// *
// * Bit  0    - writer locked bit
// * Bit  1    - waiters present bit
// * Bit  2    - lock handoff bit
// * Bits 3-7  - reserved
// * Bits 8-30 - 23-bit reader count
// * Bit  31   - read fail bit
// *
// * It is not likely that the most significant bit (read fail bit) will ever
// * be set. This guard bit is still checked anyway in the down_read() fastpath
// * just in case we need to use up more of the reader bits for other purpose
// * in the future.
// *
// * atomic_long_fetch_add() is used to obtain reader lock, whereas
// * atomic_long_cmpxchg() will be used to obtain writer lock.
// *
// * There are three places where the lock handoff bit may be set or cleared.
// * 1) rwsem_mark_wake() for readers.
// * 2) rwsem_try_write_lock() for writers.
// * 3) Error path of rwsem_down_write_slowpath().
// *
// * For all the above cases, wait_lock will be held. A writer must also
// * be the first one in the wait_list to be eligible for setting the handoff
// * bit. So concurrent setting/clearing of handoff bit is not possible.
// */
//#define RWSEM_WRITER_LOCKED	(1UL << 0)
//#define RWSEM_FLAG_WAITERS	(1UL << 1)
//#define RWSEM_FLAG_HANDOFF	(1UL << 2)
//#define RWSEM_FLAG_READFAIL	(1UL << (BITS_PER_LONG - 1))

//#define RWSEM_READER_SHIFT	8
//#define RWSEM_READER_BIAS	(1UL << RWSEM_READER_SHIFT)
//#define RWSEM_READER_MASK	(~(RWSEM_READER_BIAS - 1))
//#define RWSEM_WRITER_MASK	RWSEM_WRITER_LOCKED
//#define RWSEM_LOCK_MASK		(RWSEM_WRITER_MASK|RWSEM_READER_MASK)
//#define RWSEM_READ_FAILED_MASK	(RWSEM_WRITER_MASK|RWSEM_FLAG_WAITERS|\
//				 RWSEM_FLAG_HANDOFF|RWSEM_FLAG_READFAIL)

///*
// * All writes to owner are protected by WRITE_ONCE() to make sure that
// * store tearing can't happen as optimistic spinners may read and use
// * the owner value concurrently without lock. Read from owner, however,
// * may not need READ_ONCE() as long as the pointer value is only used
// * for comparison and isn't being dereferenced.
// */
//static inline void rwsem_set_owner(struct rw_semaphore *sem)
//{
//	atomic_long_set(&sem->owner, (long)current);
//}

//static inline void rwsem_clear_owner(struct rw_semaphore *sem)
//{
//	atomic_long_set(&sem->owner, 0);
//}

///*
// * Test the flags in the owner field.
// */
//static inline bool rwsem_test_oflags(struct rw_semaphore *sem, long flags)
//{
//	return atomic_long_read(&sem->owner) & flags;
//}

///*
// * The task_struct pointer of the last owning reader will be left in
// * the owner field.
// *
// * Note that the owner value just indicates the task has owned the rwsem
// * previously, it may not be the real owner or one of the real owners
// * anymore when that field is examined, so take it with a grain of salt.
// *
// * The reader non-spinnable bit is preserved.
// */
//static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
//					    struct task_struct *owner)
//{
//	unsigned long val = (unsigned long)owner | RWSEM_READER_OWNED |
//		(atomic_long_read(&sem->owner) & RWSEM_RD_NONSPINNABLE);

//	atomic_long_set(&sem->owner, val);
//}

//static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
//{
//	__rwsem_set_reader_owned(sem, current);
//}

///*
// * Return true if the rwsem is owned by a reader.
// */
//static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
//{
//#ifdef CONFIG_DEBUG_RWSEMS
//	/*
//	 * Check the count to see if it is write-locked.
//	 */
//	long count = atomic_long_read(&sem->count);

//	if (count & RWSEM_WRITER_MASK)
//		return false;
//#endif
//	return rwsem_test_oflags(sem, RWSEM_READER_OWNED);
//}

//#ifdef CONFIG_DEBUG_RWSEMS
///*
// * With CONFIG_DEBUG_RWSEMS configured, it will make sure that if there
// * is a task pointer in owner of a reader-owned rwsem, it will be the
// * real owner or one of the real owners. The only exception is when the
// * unlock is done by up_read_non_owner().
// */
//static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
//{
//	unsigned long val = atomic_long_read(&sem->owner);

//	while ((val & ~RWSEM_OWNER_FLAGS_MASK) == (unsigned long)current) {
//		if (atomic_long_try_cmpxchg(&sem->owner, &val,
//					    val & RWSEM_OWNER_FLAGS_MASK))
//			return;
//	}
//}
//#else
//static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
//{
//}
//#endif

///*
// * Set the RWSEM_NONSPINNABLE bits if the RWSEM_READER_OWNED flag
// * remains set. Otherwise, the operation will be aborted.
// */
//static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
//{
//	unsigned long owner = atomic_long_read(&sem->owner);

//	do {
//		if (!(owner & RWSEM_READER_OWNED))
//			break;
//		if (owner & RWSEM_NONSPINNABLE)
//			break;
//	} while (!atomic_long_try_cmpxchg(&sem->owner, &owner,
//					  owner | RWSEM_NONSPINNABLE));
//}

//static inline bool rwsem_read_trylock(struct rw_semaphore *sem)
//{
//	long cnt = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
//	if (WARN_ON_ONCE(cnt < 0))
//		rwsem_set_nonspinnable(sem);
//	return !(cnt & RWSEM_READ_FAILED_MASK);
//}

///*
// * Return just the real task structure pointer of the owner
// */
//static inline struct task_struct *rwsem_owner(struct rw_semaphore *sem)
//{
//	return (struct task_struct *)
//		(atomic_long_read(&sem->owner) & ~RWSEM_OWNER_FLAGS_MASK);
//}

///*
// * Return the real task structure pointer of the owner and the embedded
// * flags in the owner. pflags must be non-NULL.
// */
//static inline struct task_struct *
//rwsem_owner_flags(struct rw_semaphore *sem, unsigned long *pflags)
//{
//	unsigned long owner = atomic_long_read(&sem->owner);

//	*pflags = owner & RWSEM_OWNER_FLAGS_MASK;
//	return (struct task_struct *)(owner & ~RWSEM_OWNER_FLAGS_MASK);
//}

///*
// * Guide to the rw_semaphore's count field.
// *
// * When the RWSEM_WRITER_LOCKED bit in count is set, the lock is owned
// * by a writer.
// *
// * The lock is owned by readers when
// * (1) the RWSEM_WRITER_LOCKED isn't set in count,
// * (2) some of the reader bits are set in count, and
// * (3) the owner field has RWSEM_READ_OWNED bit set.
// *
// * Having some reader bits set is not enough to guarantee a readers owned
// * lock as the readers may be in the process of backing out from the count
// * and a writer has just released the lock. So another writer may steal
// * the lock immediately after that.
// */

///*
// * Initialize an rwsem:
// */
//void __init_rwsem(struct rw_semaphore *sem, const char *name,
//		  struct lock_class_key *key)
//{
//#ifdef CONFIG_DEBUG_LOCK_ALLOC
//	/*
//	 * Make sure we are not reinitializing a held semaphore:
//	 */
//	debug_check_no_locks_freed((void *)sem, sizeof(*sem));
//	lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);
//#endif
//#ifdef CONFIG_DEBUG_RWSEMS
//	sem->magic = sem;
//#endif
//	atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE);
//	raw_spin_lock_init(&sem->wait_lock);
//	INIT_LIST_HEAD(&sem->wait_list);
//	atomic_long_set(&sem->owner, 0L);
//#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
//	osq_lock_init(&sem->osq);
//#endif
//}
//EXPORT_SYMBOL(__init_rwsem);

//enum rwsem_waiter_type {
//	RWSEM_WAITING_FOR_WRITE,
//	RWSEM_WAITING_FOR_READ
//};

//struct rwsem_waiter {
//	struct list_head list;
//	struct task_struct *task;
//	enum rwsem_waiter_type type;
//	unsigned long timeout;
//	unsigned long last_rowner;
//};
//#define rwsem_first_waiter(sem) \
//	list_first_entry(&sem->wait_list, struct rwsem_waiter, list)

//enum rwsem_wake_type {
//	RWSEM_WAKE_ANY,		/* Wake whatever's at head of wait list */
//	RWSEM_WAKE_READERS,	/* Wake readers only */
//	RWSEM_WAKE_READ_OWNED	/* Waker thread holds the read lock */
//};

//enum writer_wait_state {
//	WRITER_NOT_FIRST,	/* Writer is not first in wait list */
//	WRITER_FIRST,		/* Writer is first in wait list     */
//	WRITER_HANDOFF		/* Writer is first & handoff needed */
//};

///*
// * The typical HZ value is either 250 or 1000. So set the minimum waiting
// * time to at least 4ms or 1 jiffy (if it is higher than 4ms) in the wait
// * queue before initiating the handoff protocol.
// */
//#define RWSEM_WAIT_TIMEOUT	DIV_ROUND_UP(HZ, 250)

///*
// * Magic number to batch-wakeup waiting readers, even when writers are
// * also present in the queue. This both limits the amount of work the
// * waking thread must do and also prevents any potential counter overflow,
// * however unlikely.
// */
//#define MAX_READERS_WAKEUP	0x100

///*
// * handle the lock release when processes blocked on it that can now run
// * - if we come here from up_xxxx(), then the RWSEM_FLAG_WAITERS bit must
// *   have been set.
// * - there must be someone on the queue
// * - the wait_lock must be held by the caller
// * - tasks are marked for wakeup, the caller must later invoke wake_up_q()
// *   to actually wakeup the blocked task(s) and drop the reference count,
// *   preferably when the wait_lock is released
// * - woken process blocks are discarded from the list after having task zeroed
// * - writers are only marked woken if downgrading is false
// */
//static void rwsem_mark_wake(struct rw_semaphore *sem,
//			    enum rwsem_wake_type wake_type,
//			    struct wake_q_head *wake_q)
//{
//	struct rwsem_waiter *waiter, *tmp;
//	long oldcount, woken = 0, adjustment = 0;
//	struct list_head wlist;

//	lockdep_assert_held(&sem->wait_lock);

//	/*
//	 * Take a peek at the queue head waiter such that we can determine
//	 * the wakeup(s) to perform.
//	 */
//	waiter = rwsem_first_waiter(sem);

//	if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
//		if (wake_type == RWSEM_WAKE_ANY) {
//			/*
//			 * Mark writer at the front of the queue for wakeup.
//			 * Until the task is actually later awoken later by
//			 * the caller, other writers are able to steal it.
//			 * Readers, on the other hand, will block as they
//			 * will notice the queued writer.
//			 */
//			wake_q_add(wake_q, waiter->task);
//			lockevent_inc(rwsem_wake_writer);
//		}

//		return;
//	}

//	/*
//	 * No reader wakeup if there are too many of them already.
//	 */
//	if (unlikely(atomic_long_read(&sem->count) < 0))
//		return;

//	/*
//	 * Writers might steal the lock before we grant it to the next reader.
//	 * We prefer to do the first reader grant before counting readers
//	 * so we can bail out early if a writer stole the lock.
//	 */
//	if (wake_type != RWSEM_WAKE_READ_OWNED) {
//		struct task_struct *owner;

//		adjustment = RWSEM_READER_BIAS;
//		oldcount = atomic_long_fetch_add(adjustment, &sem->count);
//		if (unlikely(oldcount & RWSEM_WRITER_MASK)) {
//			/*
//			 * When we've been waiting "too" long (for writers
//			 * to give up the lock), request a HANDOFF to
//			 * force the issue.
//			 */
//			if (!(oldcount & RWSEM_FLAG_HANDOFF) &&
//			    time_after(jiffies, waiter->timeout)) {
//				adjustment -= RWSEM_FLAG_HANDOFF;
//				lockevent_inc(rwsem_rlock_handoff);
//			}

//			atomic_long_add(-adjustment, &sem->count);
//			return;
//		}
//		/*
//		 * Set it to reader-owned to give spinners an early
//		 * indication that readers now have the lock.
//		 * The reader nonspinnable bit seen at slowpath entry of
//		 * the reader is copied over.
//		 */
//		owner = waiter->task;
//		if (waiter->last_rowner & RWSEM_RD_NONSPINNABLE) {
//			owner = (void *)((unsigned long)owner | RWSEM_RD_NONSPINNABLE);
//			lockevent_inc(rwsem_opt_norspin);
//		}
//		__rwsem_set_reader_owned(sem, owner);
//	}

//	/*
//	 * Grant up to MAX_READERS_WAKEUP read locks to all the readers in the
//	 * queue. We know that the woken will be at least 1 as we accounted
//	 * for above. Note we increment the 'active part' of the count by the
//	 * number of readers before waking any processes up.
//	 *
//	 * This is an adaptation of the phase-fair R/W locks where at the
//	 * reader phase (first waiter is a reader), all readers are eligible
//	 * to acquire the lock at the same time irrespective of their order
//	 * in the queue. The writers acquire the lock according to their
//	 * order in the queue.
//	 *
//	 * We have to do wakeup in 2 passes to prevent the possibility that
//	 * the reader count may be decremented before it is incremented. It
//	 * is because the to-be-woken waiter may not have slept yet. So it
//	 * may see waiter->task got cleared, finish its critical section and
//	 * do an unlock before the reader count increment.
//	 *
//	 * 1) Collect the read-waiters in a separate list, count them and
//	 *    fully increment the reader count in rwsem.
//	 * 2) For each waiters in the new list, clear waiter->task and
//	 *    put them into wake_q to be woken up later.
//	 */
//	INIT_LIST_HEAD(&wlist);
//	list_for_each_entry_safe(waiter, tmp, &sem->wait_list, list) {
//		if (waiter->type == RWSEM_WAITING_FOR_WRITE)
//			continue;

//		woken++;
//		list_move_tail(&waiter->list, &wlist);

//		/*
//		 * Limit # of readers that can be woken up per wakeup call.
//		 */
//		if (woken >= MAX_READERS_WAKEUP)
//			break;
//	}

//	adjustment = woken * RWSEM_READER_BIAS - adjustment;
//	lockevent_cond_inc(rwsem_wake_reader, woken);
//	if (list_empty(&sem->wait_list)) {
//		/* hit end of list above */
//		adjustment -= RWSEM_FLAG_WAITERS;
//	}

//	/*
//	 * When we've woken a reader, we no longer need to force writers
//	 * to give up the lock and we can clear HANDOFF.
//	 */
//	if (woken && (atomic_long_read(&sem->count) & RWSEM_FLAG_HANDOFF))
//		adjustment -= RWSEM_FLAG_HANDOFF;

//	if (adjustment)
//		atomic_long_add(adjustment, &sem->count);

//	/* 2nd pass */
//	list_for_each_entry_safe(waiter, tmp, &wlist, list) {
//		struct task_struct *tsk;

//		tsk = waiter->task;
//		get_task_struct(tsk);

//		/*
//		 * Ensure calling get_task_struct() before setting the reader
//		 * waiter to nil such that rwsem_down_read_slowpath() cannot
//		 * race with do_exit() by always holding a reference count
//		 * to the task to wakeup.
//		 */
//		smp_store_release(&waiter->task, NULL);
//		/*
//		 * Ensure issuing the wakeup (either by us or someone else)
//		 * after setting the reader waiter to nil.
//		 */
//		wake_q_add_safe(wake_q, tsk);
//	}
//}

///*
// * This function must be called with the sem->wait_lock held to prevent
// * race conditions between checking the rwsem wait list and setting the
// * sem->count accordingly.
// *
// * If wstate is WRITER_HANDOFF, it will make sure that either the handoff
// * bit is set or the lock is acquired with handoff bit cleared.
// */
//static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
//					enum writer_wait_state wstate)
//{
//	long count, new;

//	lockdep_assert_held(&sem->wait_lock);

//	count = atomic_long_read(&sem->count);
//	do {
//		bool has_handoff = !!(count & RWSEM_FLAG_HANDOFF);

//		if (has_handoff && wstate == WRITER_NOT_FIRST)
//			return false;

//		new = count;

//		if (count & RWSEM_LOCK_MASK) {
//			if (has_handoff || (wstate != WRITER_HANDOFF))
//				return false;

//			new |= RWSEM_FLAG_HANDOFF;
//		} else {
//			new |= RWSEM_WRITER_LOCKED;
//			new &= ~RWSEM_FLAG_HANDOFF;

//			if (list_is_singular(&sem->wait_list))
//				new &= ~RWSEM_FLAG_WAITERS;
//		}
//	} while (!atomic_long_try_cmpxchg_acquire(&sem->count, &count, new));

//	/*
//	 * We have either acquired the lock with handoff bit cleared or
//	 * set the handoff bit.
//	 */
//	if (new & RWSEM_FLAG_HANDOFF)
//		return false;

//	rwsem_set_owner(sem);
//	return true;
//}

//#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
///*
// * Try to acquire read lock before the reader is put on wait queue.
// * Lock acquisition isn't allowed if the rwsem is locked or a writer handoff
// * is ongoing.
// */
//static inline bool rwsem_try_read_lock_unqueued(struct rw_semaphore *sem)
//{
//	long count = atomic_long_read(&sem->count);

//	if (count & (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))
//		return false;

//	count = atomic_long_fetch_add_acquire(RWSEM_READER_BIAS, &sem->count);
//	if (!(count & (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {
//		rwsem_set_reader_owned(sem);
//		lockevent_inc(rwsem_opt_rlock);
//		return true;
//	}

//	/* Back out the change */
//	atomic_long_add(-RWSEM_READER_BIAS, &sem->count);
//	return false;
//}

///*
// * Try to acquire write lock before the writer has been put on wait queue.
// */
//static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
//{
//	long count = atomic_long_read(&sem->count);

//	while (!(count & (RWSEM_LOCK_MASK|RWSEM_FLAG_HANDOFF))) {
//		if (atomic_long_try_cmpxchg_acquire(&sem->count, &count,
//					count | RWSEM_WRITER_LOCKED)) {
//			rwsem_set_owner(sem);
//			lockevent_inc(rwsem_opt_wlock);
//			return true;
//		}
//	}
//	return false;
//}

//static inline bool owner_on_cpu(struct task_struct *owner)
//{
//	/*
//	 * As lock holder preemption issue, we both skip spinning if
//	 * task is not on cpu or its cpu is preempted
//	 */
//	return owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
//}

//static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem,
//					   unsigned long nonspinnable)
//{
//	struct task_struct *owner;
//	unsigned long flags;
//	bool ret = true;

//	if (need_resched()) {
//		lockevent_inc(rwsem_opt_fail);
//		return false;
//	}

//	preempt_disable();
//	rcu_read_lock();
//	owner = rwsem_owner_flags(sem, &flags);
//	/*
//	 * Don't check the read-owner as the entry may be stale.
//	 */
//	if ((flags & nonspinnable) ||
//	    (owner && !(flags & RWSEM_READER_OWNED) && !owner_on_cpu(owner)))
//		ret = false;
//	rcu_read_unlock();
//	preempt_enable();

//	lockevent_cond_inc(rwsem_opt_fail, !ret);
//	return ret;
//}

///*
// * The rwsem_spin_on_owner() function returns the folowing 4 values
// * depending on the lock owner state.
// *   OWNER_NULL  : owner is currently NULL
// *   OWNER_WRITER: when owner changes and is a writer
// *   OWNER_READER: when owner changes and the new owner may be a reader.
// *   OWNER_NONSPINNABLE:
// *		   when optimistic spinning has to stop because either the
// *		   owner stops running, is unknown, or its timeslice has
// *		   been used up.
// */
//enum owner_state {
//	OWNER_NULL		= 1 << 0,
//	OWNER_WRITER		= 1 << 1,
//	OWNER_READER		= 1 << 2,
//	OWNER_NONSPINNABLE	= 1 << 3,
//};
//#define OWNER_SPINNABLE		(OWNER_NULL | OWNER_WRITER | OWNER_READER)

//static inline enum owner_state
//rwsem_owner_state(struct task_struct *owner, unsigned long flags, unsigned long nonspinnable)
//{
//	if (flags & nonspinnable)
//		return OWNER_NONSPINNABLE;

//	if (flags & RWSEM_READER_OWNED)
//		return OWNER_READER;

//	return owner ? OWNER_WRITER : OWNER_NULL;
//}

//static noinline enum owner_state
//rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
//{
//	struct task_struct *new, *owner;
//	unsigned long flags, new_flags;
//	enum owner_state state;

//	owner = rwsem_owner_flags(sem, &flags);
//	state = rwsem_owner_state(owner, flags, nonspinnable);
//	if (state != OWNER_WRITER)
//		return state;

//	rcu_read_lock();
//	for (;;) {
//		/*
//		 * When a waiting writer set the handoff flag, it may spin
//		 * on the owner as well. Once that writer acquires the lock,
//		 * we can spin on it. So we don't need to quit even when the
//		 * handoff bit is set.
//		 */
//		new = rwsem_owner_flags(sem, &new_flags);
//		if ((new != owner) || (new_flags != flags)) {
//			state = rwsem_owner_state(new, new_flags, nonspinnable);
//			break;
//		}

//		/*
//		 * Ensure we emit the owner->on_cpu, dereference _after_
//		 * checking sem->owner still matches owner, if that fails,
//		 * owner might point to free()d memory, if it still matches,
//		 * the rcu_read_lock() ensures the memory stays valid.
//		 */
//		barrier();

//		if (need_resched() || !owner_on_cpu(owner)) {
//			state = OWNER_NONSPINNABLE;
//			break;
//		}

//		cpu_relax();
//	}
//	rcu_read_unlock();

//	return state;
//}

///*
// * Calculate reader-owned rwsem spinning threshold for writer
// *
// * The more readers own the rwsem, the longer it will take for them to
// * wind down and free the rwsem. So the empirical formula used to
// * determine the actual spinning time limit here is:
// *
// *   Spinning threshold = (10 + nr_readers/2)us
// *
// * The limit is capped to a maximum of 25us (30 readers). This is just
// * a heuristic and is subjected to change in the future.
// */
//static inline u64 rwsem_rspin_threshold(struct rw_semaphore *sem)
//{
//	long count = atomic_long_read(&sem->count);
//	int readers = count >> RWSEM_READER_SHIFT;
//	u64 delta;

//	if (readers > 30)
//		readers = 30;
//	delta = (20 + readers) * NSEC_PER_USEC / 2;

//	return sched_clock() + delta;
//}

//static bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
//{
//	bool taken = false;
//	int prev_owner_state = OWNER_NULL;
//	int loop = 0;
//	u64 rspin_threshold = 0;
//	unsigned long nonspinnable = wlock ? RWSEM_WR_NONSPINNABLE
//					   : RWSEM_RD_NONSPINNABLE;

//	preempt_disable();

//	/* sem->wait_lock should not be held when doing optimistic spinning */
//	if (!osq_lock(&sem->osq))
//		goto done;

//	/*
//	 * Optimistically spin on the owner field and attempt to acquire the
//	 * lock whenever the owner changes. Spinning will be stopped when:
//	 *  1) the owning writer isn't running; or
//	 *  2) readers own the lock and spinning time has exceeded limit.
//	 */
//	for (;;) {
//		enum owner_state owner_state;

//		owner_state = rwsem_spin_on_owner(sem, nonspinnable);
//		if (!(owner_state & OWNER_SPINNABLE))
//			break;

//		/*
//		 * Try to acquire the lock
//		 */
//		taken = wlock ? rwsem_try_write_lock_unqueued(sem)
//			      : rwsem_try_read_lock_unqueued(sem);

//		if (taken)
//			break;

//		/*
//		 * Time-based reader-owned rwsem optimistic spinning
//		 */
//		if (wlock && (owner_state == OWNER_READER)) {
//			/*
//			 * Re-initialize rspin_threshold every time when
//			 * the owner state changes from non-reader to reader.
//			 * This allows a writer to steal the lock in between
//			 * 2 reader phases and have the threshold reset at
//			 * the beginning of the 2nd reader phase.
//			 */
//			if (prev_owner_state != OWNER_READER) {
//				if (rwsem_test_oflags(sem, nonspinnable))
//					break;
//				rspin_threshold = rwsem_rspin_threshold(sem);
//				loop = 0;
//			}

//			/*
//			 * Check time threshold once every 16 iterations to
//			 * avoid calling sched_clock() too frequently so
//			 * as to reduce the average latency between the times
//			 * when the lock becomes free and when the spinner
//			 * is ready to do a trylock.
//			 */
//			else if (!(++loop & 0xf) && (sched_clock() > rspin_threshold)) {
//				rwsem_set_nonspinnable(sem);
//				lockevent_inc(rwsem_opt_nospin);
//				break;
//			}
//		}

//		/*
//		 * An RT task cannot do optimistic spinning if it cannot
//		 * be sure the lock holder is running or live-lock may
//		 * happen if the current task and the lock holder happen
//		 * to run in the same CPU. However, aborting optimistic
//		 * spinning while a NULL owner is detected may miss some
//		 * opportunity where spinning can continue without causing
//		 * problem.
//		 *
//		 * There are 2 possible cases where an RT task may be able
//		 * to continue spinning.
//		 *
//		 * 1) The lock owner is in the process of releasing the
//		 *    lock, sem->owner is cleared but the lock has not
//		 *    been released yet.
//		 * 2) The lock was free and owner cleared, but another
//		 *    task just comes in and acquire the lock before
//		 *    we try to get it. The new owner may be a spinnable
//		 *    writer.
//		 *
//		 * To take advantage of two scenarios listed agove, the RT
//		 * task is made to retry one more time to see if it can
//		 * acquire the lock or continue spinning on the new owning
//		 * writer. Of course, if the time lag is long enough or the
//		 * new owner is not a writer or spinnable, the RT task will
//		 * quit spinning.
//		 *
//		 * If the owner is a writer, the need_resched() check is
//		 * done inside rwsem_spin_on_owner(). If the owner is not
//		 * a writer, need_resched() check needs to be done here.
//		 */
//		if (owner_state != OWNER_WRITER) {
//			if (need_resched())
//				break;
//			if (rt_task(current) &&
//			   (prev_owner_state != OWNER_WRITER))
//				break;
//		}
//		prev_owner_state = owner_state;

//		/*
//		 * The cpu_relax() call is a compiler barrier which forces
//		 * everything in this loop to be re-loaded. We don't need
//		 * memory barriers as we'll eventually observe the right
//		 * values at the cost of a few extra spins.
//		 */
//		cpu_relax();
//	}
//	osq_unlock(&sem->osq);
//done:
//	preempt_enable();
//	lockevent_cond_inc(rwsem_opt_fail, !taken);
//	return taken;
//}

///*
// * Clear the owner's RWSEM_WR_NONSPINNABLE bit if it is set. This should
// * only be called when the reader count reaches 0.
// *
// * This give writers better chance to acquire the rwsem first before
// * readers when the rwsem was being held by readers for a relatively long
// * period of time. Race can happen that an optimistic spinner may have
// * just stolen the rwsem and set the owner, but just clearing the
// * RWSEM_WR_NONSPINNABLE bit will do no harm anyway.
// */
//static inline void clear_wr_nonspinnable(struct rw_semaphore *sem)
//{
//	if (rwsem_test_oflags(sem, RWSEM_WR_NONSPINNABLE))
//		atomic_long_andnot(RWSEM_WR_NONSPINNABLE, &sem->owner);
//}

///*
// * This function is called when the reader fails to acquire the lock via
// * optimistic spinning. In this case we will still attempt to do a trylock
// * when comparing the rwsem state right now with the state when entering
// * the slowpath indicates that the reader is still in a valid reader phase.
// * This happens when the following conditions are true:
// *
// * 1) The lock is currently reader owned, and
// * 2) The lock is previously not reader-owned or the last read owner changes.
// *
// * In the former case, we have transitioned from a writer phase to a
// * reader-phase while spinning. In the latter case, it means the reader
// * phase hasn't ended when we entered the optimistic spinning loop. In
// * both cases, the reader is eligible to acquire the lock. This is the
// * secondary path where a read lock is acquired optimistically.
// *
// * The reader non-spinnable bit wasn't set at time of entry or it will
// * not be here at all.
// */
//static inline bool rwsem_reader_phase_trylock(struct rw_semaphore *sem,
//					      unsigned long last_rowner)
//{
//	unsigned long owner = atomic_long_read(&sem->owner);

//	if (!(owner & RWSEM_READER_OWNED))
//		return false;

//	if (((owner ^ last_rowner) & ~RWSEM_OWNER_FLAGS_MASK) &&
//	    rwsem_try_read_lock_unqueued(sem)) {
//		lockevent_inc(rwsem_opt_rlock2);
//		lockevent_add(rwsem_opt_fail, -1);
//		return true;
//	}
//	return false;
//}
//#else
//static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem,
//					   unsigned long nonspinnable)
//{
//	return false;
//}

//static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
//{
//	return false;
//}

//static inline void clear_wr_nonspinnable(struct rw_semaphore *sem) { }

//static inline bool rwsem_reader_phase_trylock(struct rw_semaphore *sem,
//					      unsigned long last_rowner)
//{
//	return false;
//}

//static inline int
//rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
//{
//	return 0;
//}
//#define OWNER_NULL	1
//#endif

///*
// * Wait for the read lock to be granted
// */
//static struct rw_semaphore __sched *
//rwsem_down_read_slowpath(struct rw_semaphore *sem, int state)
//{
//	long count, adjustment = -RWSEM_READER_BIAS;
//	struct rwsem_waiter waiter;
//	DEFINE_WAKE_Q(wake_q);
//	bool wake = false;

//	/*
//	 * Save the current read-owner of rwsem, if available, and the
//	 * reader nonspinnable bit.
//	 */
//	waiter.last_rowner = atomic_long_read(&sem->owner);
//	if (!(waiter.last_rowner & RWSEM_READER_OWNED))
//		waiter.last_rowner &= RWSEM_RD_NONSPINNABLE;

//	if (!rwsem_can_spin_on_owner(sem, RWSEM_RD_NONSPINNABLE))
//		goto queue;

//	/*
//	 * Undo read bias from down_read() and do optimistic spinning.
//	 */
//	atomic_long_add(-RWSEM_READER_BIAS, &sem->count);
//	adjustment = 0;
//	if (rwsem_optimistic_spin(sem, false)) {
//		/* rwsem_optimistic_spin() implies ACQUIRE on success */
//		/*
//		 * Wake up other readers in the wait list if the front
//		 * waiter is a reader.
//		 */
//		if ((atomic_long_read(&sem->count) & RWSEM_FLAG_WAITERS)) {
//			raw_spin_lock_irq(&sem->wait_lock);
//			if (!list_empty(&sem->wait_list))
//				rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED,
//						&wake_q);
//			raw_spin_unlock_irq(&sem->wait_lock);
//			wake_up_q(&wake_q);
//		}
//		return sem;
//	} else if (rwsem_reader_phase_trylock(sem, waiter.last_rowner)) {
//		/* rwsem_reader_phase_trylock() implies ACQUIRE on success */
//		return sem;
//	}

//queue:
//	waiter.task = current;
//	waiter.type = RWSEM_WAITING_FOR_READ;
//	waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;

//	raw_spin_lock_irq(&sem->wait_lock);
//	if (list_empty(&sem->wait_list)) {
//		/*
//		 * In case the wait queue is empty and the lock isn't owned
//		 * by a writer or has the handoff bit set, this reader can
//		 * exit the slowpath and return immediately as its
//		 * RWSEM_READER_BIAS has already been set in the count.
//		 */
//		if (adjustment && !(atomic_long_read(&sem->count) &
//		     (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {
//			/* Provide lock ACQUIRE */
//			smp_acquire__after_ctrl_dep();
//			raw_spin_unlock_irq(&sem->wait_lock);
//			rwsem_set_reader_owned(sem);
//			lockevent_inc(rwsem_rlock_fast);
//			return sem;
//		}
//		adjustment += RWSEM_FLAG_WAITERS;
//	}
//	list_add_tail(&waiter.list, &sem->wait_list);

//	/* we're now waiting on the lock, but no longer actively locking */
//	if (adjustment)
//		count = atomic_long_add_return(adjustment, &sem->count);
//	else
//		count = atomic_long_read(&sem->count);

//	/*
//	 * If there are no active locks, wake the front queued process(es).
//	 *
//	 * If there are no writers and we are first in the queue,
//	 * wake our own waiter to join the existing active readers !
//	 */
//	if (!(count & RWSEM_LOCK_MASK)) {
//		clear_wr_nonspinnable(sem);
//		wake = true;
//	}
//	if (wake || (!(count & RWSEM_WRITER_MASK) &&
//		    (adjustment & RWSEM_FLAG_WAITERS)))
//		rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);

//	raw_spin_unlock_irq(&sem->wait_lock);
//	wake_up_q(&wake_q);

//	/* wait to be given the lock */
//	for (;;) {
//		set_current_state(state);
//		if (!smp_load_acquire(&waiter.task)) {
//			/* Matches rwsem_mark_wake()'s smp_store_release(). */
//			break;
//		}
//		if (signal_pending_state(state, current)) {
//			raw_spin_lock_irq(&sem->wait_lock);
//			if (waiter.task)
//				goto out_nolock;
//			raw_spin_unlock_irq(&sem->wait_lock);
//			/* Ordered by sem->wait_lock against rwsem_mark_wake(). */
//			break;
//		}
//		schedule();
//		lockevent_inc(rwsem_sleep_reader);
//	}

//	__set_current_state(TASK_RUNNING);
//	lockevent_inc(rwsem_rlock);
//	return sem;

//out_nolock:
//	list_del(&waiter.list);
//	if (list_empty(&sem->wait_list)) {
//		atomic_long_andnot(RWSEM_FLAG_WAITERS|RWSEM_FLAG_HANDOFF,
//				   &sem->count);
//	}
//	raw_spin_unlock_irq(&sem->wait_lock);
//	__set_current_state(TASK_RUNNING);
//	lockevent_inc(rwsem_rlock_fail);
//	return ERR_PTR(-EINTR);
//}

///*
// * This function is called by the a write lock owner. So the owner value
// * won't get changed by others.
// */
//static inline void rwsem_disable_reader_optspin(struct rw_semaphore *sem,
//						bool disable)
//{
//	if (unlikely(disable)) {
//		atomic_long_or(RWSEM_RD_NONSPINNABLE, &sem->owner);
//		lockevent_inc(rwsem_opt_norspin);
//	}
//}

///*
// * Wait until we successfully acquire the write lock
// */
//static struct rw_semaphore *
//rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
//{
//	long count;
//	bool disable_rspin;
//	enum writer_wait_state wstate;
//	struct rwsem_waiter waiter;
//	struct rw_semaphore *ret = sem;
//	DEFINE_WAKE_Q(wake_q);

//	/* do optimistic spinning and steal lock if possible */
//	if (rwsem_can_spin_on_owner(sem, RWSEM_WR_NONSPINNABLE) &&
//	    rwsem_optimistic_spin(sem, true)) {
//		/* rwsem_optimistic_spin() implies ACQUIRE on success */
//		return sem;
//	}

//	/*
//	 * Disable reader optimistic spinning for this rwsem after
//	 * acquiring the write lock when the setting of the nonspinnable
//	 * bits are observed.
//	 */
//	disable_rspin = atomic_long_read(&sem->owner) & RWSEM_NONSPINNABLE;

//	/*
//	 * Optimistic spinning failed, proceed to the slowpath
//	 * and block until we can acquire the sem.
//	 */
//	waiter.task = current;
//	waiter.type = RWSEM_WAITING_FOR_WRITE;
//	waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;

//	raw_spin_lock_irq(&sem->wait_lock);

//	/* account for this before adding a new element to the list */
//	wstate = list_empty(&sem->wait_list) ? WRITER_FIRST : WRITER_NOT_FIRST;

//	list_add_tail(&waiter.list, &sem->wait_list);

//	/* we're now waiting on the lock */
//	if (wstate == WRITER_NOT_FIRST) {
//		count = atomic_long_read(&sem->count);

//		/*
//		 * If there were already threads queued before us and:
//		 *  1) there are no no active locks, wake the front
//		 *     queued process(es) as the handoff bit might be set.
//		 *  2) there are no active writers and some readers, the lock
//		 *     must be read owned; so we try to wake any read lock
//		 *     waiters that were queued ahead of us.
//		 */
//		if (count & RWSEM_WRITER_MASK)
//			goto wait;

//		rwsem_mark_wake(sem, (count & RWSEM_READER_MASK)
//					? RWSEM_WAKE_READERS
//					: RWSEM_WAKE_ANY, &wake_q);

//		if (!wake_q_empty(&wake_q)) {
//			/*
//			 * We want to minimize wait_lock hold time especially
//			 * when a large number of readers are to be woken up.
//			 */
//			raw_spin_unlock_irq(&sem->wait_lock);
//			wake_up_q(&wake_q);
//			wake_q_init(&wake_q);	/* Used again, reinit */
//			raw_spin_lock_irq(&sem->wait_lock);
//		}
//	} else {
//		atomic_long_or(RWSEM_FLAG_WAITERS, &sem->count);
//	}

//wait:
//	/* wait until we successfully acquire the lock */
//	set_current_state(state);
//	for (;;) {
//		if (rwsem_try_write_lock(sem, wstate)) {
//			/* rwsem_try_write_lock() implies ACQUIRE on success */
//			break;
//		}

//		raw_spin_unlock_irq(&sem->wait_lock);

//		/*
//		 * After setting the handoff bit and failing to acquire
//		 * the lock, attempt to spin on owner to accelerate lock
//		 * transfer. If the previous owner is a on-cpu writer and it
//		 * has just released the lock, OWNER_NULL will be returned.
//		 * In this case, we attempt to acquire the lock again
//		 * without sleeping.
//		 */
//		if (wstate == WRITER_HANDOFF &&
//		    rwsem_spin_on_owner(sem, RWSEM_NONSPINNABLE) == OWNER_NULL)
//			goto trylock_again;

//		/* Block until there are no active lockers. */
//		for (;;) {
//			if (signal_pending_state(state, current))
//				goto out_nolock;

//			schedule();
//			lockevent_inc(rwsem_sleep_writer);
//			set_current_state(state);
//			/*
//			 * If HANDOFF bit is set, unconditionally do
//			 * a trylock.
//			 */
//			if (wstate == WRITER_HANDOFF)
//				break;

//			if ((wstate == WRITER_NOT_FIRST) &&
//			    (rwsem_first_waiter(sem) == &waiter))
//				wstate = WRITER_FIRST;

//			count = atomic_long_read(&sem->count);
//			if (!(count & RWSEM_LOCK_MASK))
//				break;

//			/*
//			 * The setting of the handoff bit is deferred
//			 * until rwsem_try_write_lock() is called.
//			 */
//			if ((wstate == WRITER_FIRST) && (rt_task(current) ||
//			    time_after(jiffies, waiter.timeout))) {
//				wstate = WRITER_HANDOFF;
//				lockevent_inc(rwsem_wlock_handoff);
//				break;
//			}
//		}
//trylock_again:
//		raw_spin_lock_irq(&sem->wait_lock);
//	}
//	__set_current_state(TASK_RUNNING);
//	list_del(&waiter.list);
//	rwsem_disable_reader_optspin(sem, disable_rspin);
//	raw_spin_unlock_irq(&sem->wait_lock);
//	lockevent_inc(rwsem_wlock);

//	return ret;

//out_nolock:
//	__set_current_state(TASK_RUNNING);
//	raw_spin_lock_irq(&sem->wait_lock);
//	list_del(&waiter.list);

//	if (unlikely(wstate == WRITER_HANDOFF))
//		atomic_long_add(-RWSEM_FLAG_HANDOFF,  &sem->count);

//	if (list_empty(&sem->wait_list))
//		atomic_long_andnot(RWSEM_FLAG_WAITERS, &sem->count);
//	else
//		rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
//	raw_spin_unlock_irq(&sem->wait_lock);
//	wake_up_q(&wake_q);
//	lockevent_inc(rwsem_wlock_fail);

//	return ERR_PTR(-EINTR);
//}

///*
// * handle waking up a waiter on the semaphore
// * - up_read/up_write has decremented the active part of count if we come here
// */
//static struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem, long count)
//{
//	unsigned long flags;
//	DEFINE_WAKE_Q(wake_q);

//	raw_spin_lock_irqsave(&sem->wait_lock, flags);

//	if (!list_empty(&sem->wait_list))
//		rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);

//	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
//	wake_up_q(&wake_q);

//	return sem;
//}

///*
// * downgrade a write lock into a read lock
// * - caller incremented waiting part of count and discovered it still negative
// * - just wake up any readers at the front of the queue
// */
//static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
//{
//	unsigned long flags;
//	DEFINE_WAKE_Q(wake_q);

//	raw_spin_lock_irqsave(&sem->wait_lock, flags);

//	if (!list_empty(&sem->wait_list))
//		rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q);

//	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
//	wake_up_q(&wake_q);

//	return sem;
//}

///*
// * lock for reading
// */
//static inline void __down_read(struct rw_semaphore *sem)
//{
//	if (!rwsem_read_trylock(sem)) {
//		rwsem_down_read_slowpath(sem, TASK_UNINTERRUPTIBLE);
//		DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
//	} else {
//		rwsem_set_reader_owned(sem);
//	}
//}

//static inline int __down_read_interruptible(struct rw_semaphore *sem)
//{
//	if (!rwsem_read_trylock(sem)) {
//		if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_INTERRUPTIBLE)))
//			return -EINTR;
//		DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
//	} else {
//		rwsem_set_reader_owned(sem);
//	}
//	return 0;
//}

//static inline int __down_read_killable(struct rw_semaphore *sem)
//{
//	if (!rwsem_read_trylock(sem)) {
//		if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_KILLABLE)))
//			return -EINTR;
//		DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
//	} else {
//		rwsem_set_reader_owned(sem);
//	}
//	return 0;
//}

//static inline int __down_read_trylock(struct rw_semaphore *sem)
//{
//	long tmp;

//	DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);

//	/*
//	 * Optimize for the case when the rwsem is not locked at all.
//	 */
//	tmp = RWSEM_UNLOCKED_VALUE;
//	do {
//		if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
//					tmp + RWSEM_READER_BIAS)) {
//			rwsem_set_reader_owned(sem);
//			return 1;
//		}
//	} while (!(tmp & RWSEM_READ_FAILED_MASK));
//	return 0;
//}

///*
// * lock for writing
// */
//static inline void __down_write(struct rw_semaphore *sem)
//{
//	long tmp = RWSEM_UNLOCKED_VALUE;

//	if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
//						      RWSEM_WRITER_LOCKED)))
//		rwsem_down_write_slowpath(sem, TASK_UNINTERRUPTIBLE);
//	else
//		rwsem_set_owner(sem);
//}

//static inline int __down_write_killable(struct rw_semaphore *sem)
//{
//	long tmp = RWSEM_UNLOCKED_VALUE;

//	if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
//						      RWSEM_WRITER_LOCKED))) {
//		if (IS_ERR(rwsem_down_write_slowpath(sem, TASK_KILLABLE)))
//			return -EINTR;
//	} else {
//		rwsem_set_owner(sem);
//	}
//	return 0;
//}

//static inline int __down_write_trylock(struct rw_semaphore *sem)
//{
//	long tmp;

//	DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);

//	tmp  = RWSEM_UNLOCKED_VALUE;
//	if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
//					    RWSEM_WRITER_LOCKED)) {
//		rwsem_set_owner(sem);
//		return true;
//	}
//	return false;
//}

///*
// * unlock after reading
// */
//static inline void __up_read(struct rw_semaphore *sem)
//{
//	long tmp;

//	DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
//	DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);

//	rwsem_clear_reader_owned(sem);
//	tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count);
//	DEBUG_RWSEMS_WARN_ON(tmp < 0, sem);
//	if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) ==
//		      RWSEM_FLAG_WAITERS)) {
//		clear_wr_nonspinnable(sem);
//		rwsem_wake(sem, tmp);
//	}
//}

///*
// * unlock after writing
// */
//static inline void __up_write(struct rw_semaphore *sem)
//{
//	long tmp;

//	DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
//	/*
//	 * sem->owner may differ from current if the ownership is transferred
//	 * to an anonymous writer by setting the RWSEM_NONSPINNABLE bits.
//	 */
//	DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) &&
//			    !rwsem_test_oflags(sem, RWSEM_NONSPINNABLE), sem);

//	rwsem_clear_owner(sem);
//	tmp = atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED, &sem->count);
//	if (unlikely(tmp & RWSEM_FLAG_WAITERS))
//		rwsem_wake(sem, tmp);
//}

///*
// * downgrade write lock to read lock
// */
//static inline void __downgrade_write(struct rw_semaphore *sem)
//{
//	long tmp;

//	/*
//	 * When downgrading from exclusive to shared ownership,
//	 * anything inside the write-locked region cannot leak
//	 * into the read side. In contrast, anything in the
//	 * read-locked region is ok to be re-ordered into the
//	 * write side. As such, rely on RELEASE semantics.
//	 */
//	DEBUG_RWSEMS_WARN_ON(rwsem_owner(sem) != current, sem);
//	tmp = atomic_long_fetch_add_release(
//		-RWSEM_WRITER_LOCKED+RWSEM_READER_BIAS, &sem->count);
//	rwsem_set_reader_owned(sem);
//	if (tmp & RWSEM_FLAG_WAITERS)
//		rwsem_downgrade_wake(sem);
//}

/*
 * lock for reading
 */
void __sched down_read(struct rw_semaphore *sem)
{
//	might_sleep();
//	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);

//	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
}
EXPORT_SYMBOL(down_read);

//int __sched down_read_interruptible(struct rw_semaphore *sem)
//{
//	might_sleep();
//	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);

//	if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_interruptible)) {
//		rwsem_release(&sem->dep_map, _RET_IP_);
//		return -EINTR;
//	}

//	return 0;
//}
//EXPORT_SYMBOL(down_read_interruptible);

//int __sched down_read_killable(struct rw_semaphore *sem)
//{
//	might_sleep();
//	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);

//	if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
//		rwsem_release(&sem->dep_map, _RET_IP_);
//		return -EINTR;
//	}

//	return 0;
//}
//EXPORT_SYMBOL(down_read_killable);

///*
// * trylock for reading -- returns 1 if successful, 0 if contention
// */
//int down_read_trylock(struct rw_semaphore *sem)
//{
//	int ret = __down_read_trylock(sem);

//	if (ret == 1)
//		rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
//	return ret;
//}
//EXPORT_SYMBOL(down_read_trylock);

/*
 * lock for writing
 */
void __sched down_write(struct rw_semaphore *sem)
{
//	might_sleep();
//	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
//	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
}
EXPORT_SYMBOL(down_write);

///*
// * lock for writing
// */
//int __sched down_write_killable(struct rw_semaphore *sem)
//{
//	might_sleep();
//	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);

//	if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
//				  __down_write_killable)) {
//		rwsem_release(&sem->dep_map, _RET_IP_);
//		return -EINTR;
//	}

//	return 0;
//}
//EXPORT_SYMBOL(down_write_killable);

///*
// * trylock for writing -- returns 1 if successful, 0 if contention
// */
//int down_write_trylock(struct rw_semaphore *sem)
//{
//	int ret = __down_write_trylock(sem);

//	if (ret == 1)
//		rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);

//	return ret;
//}
//EXPORT_SYMBOL(down_write_trylock);

/*
 * release a read lock
 */
void up_read(struct rw_semaphore *sem)
{
//	rwsem_release(&sem->dep_map, _RET_IP_);
//	__up_read(sem);
}
EXPORT_SYMBOL(up_read);

/*
 * release a write lock
 */
void up_write(struct rw_semaphore *sem)
{
//	rwsem_release(&sem->dep_map, _RET_IP_);
//	__up_write(sem);
}
EXPORT_SYMBOL(up_write);

///*
// * downgrade write lock to read lock
// */
//void downgrade_write(struct rw_semaphore *sem)
//{
//	lock_downgrade(&sem->dep_map, _RET_IP_);
//	__downgrade_write(sem);
//}
//EXPORT_SYMBOL(downgrade_write);

//#ifdef CONFIG_DEBUG_LOCK_ALLOC

//void down_read_nested(struct rw_semaphore *sem, int subclass)
//{
//	might_sleep();
//	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
//	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
//}
//EXPORT_SYMBOL(down_read_nested);

//int down_read_killable_nested(struct rw_semaphore *sem, int subclass)
//{
//	might_sleep();
//	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);

//	if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
//		rwsem_release(&sem->dep_map, _RET_IP_);
//		return -EINTR;
//	}

//	return 0;
//}
//EXPORT_SYMBOL(down_read_killable_nested);

//void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
//{
//	might_sleep();
//	rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_);
//	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
//}
//EXPORT_SYMBOL(_down_write_nest_lock);

//void down_read_non_owner(struct rw_semaphore *sem)
//{
//	might_sleep();
//	__down_read(sem);
//	__rwsem_set_reader_owned(sem, NULL);
//}
//EXPORT_SYMBOL(down_read_non_owner);

//void down_write_nested(struct rw_semaphore *sem, int subclass)
//{
//	might_sleep();
//	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
//	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
//}
//EXPORT_SYMBOL(down_write_nested);

//int __sched down_write_killable_nested(struct rw_semaphore *sem, int subclass)
//{
//	might_sleep();
//	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);

//	if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
//				  __down_write_killable)) {
//		rwsem_release(&sem->dep_map, _RET_IP_);
//		return -EINTR;
//	}

//	return 0;
//}
//EXPORT_SYMBOL(down_write_killable_nested);

//void up_read_non_owner(struct rw_semaphore *sem)
//{
//	DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
//	__up_read(sem);
//}
//EXPORT_SYMBOL(up_read_non_owner);

//#endif
